The invention relates to an arrangement for temperature measurement at an oxygen probe, in particular a lambda probe, having a solid electrolyte arranged between two electrodes.
Oxygen probes are known. They have an ionically conducting solid electrolyte located between two electrodes. The two electrodes are in this case gas-permeable and a measurement voltage can be applied to them. Depending on the oxygen content in the gas to be measured, a limit current or a Nernst voltage is set, which are dependent on the difference in the oxygen concentrations at the electrodes. Oxygen probes of this type are used, for example, as lambda probes in motor vehicles, in order to measure a specific oxygen content of the exhaust gas of internal combustion engines.
In the active range, oxygen probes must be heated to temperatures above approximately 300.degree. C. in order to obtain the necessary ionic conductivity of the solid electrolyte. Since the signal from the oxygen probe is dependent, amongst other things, on the temperature of the oxygen probe, temperature and velocity fluctuations of the gas to be measured are frequently so large that the temperature of the measurement probe must be monitored and, if necessary, regulated in order to obtain an increase in the measurement accuracy.
In order to regulate the temperature at the measurement probe, it is known to assign to the measurement probe a probe heater which can be switched on or off as a function of a temperature measured at the oxygen probe. In this case, use is made of the effect that the internal resistance of the oxygen probe is temperature-dependent and the temperature of the oxygen probe can be deduced using the magnitude of this internal resistance. For this purpose, it is known to load the probe signal with a defined resistance and to calculate the internal resistance from the resulting load voltage. It is further known to impress an AC voltage on the probe signal using a known resistance and to calculate the AC impedance from the voltage drop across the oxygen probe. Furthermore, an alternating current of known amplitude can be superimposed on the probe signal and the AC impedance can be calculated from the reaction of the probe voltage amplitude.
In the known devices for temperature measurement, it is disadvantageous that they can be produced only at great expense using a multiplicity of components and in the end only a temperature of the solid electrolyte can be determined. However, a signal voltage from the oxygen probe is, in addition to the temperature of the solid electrolyte, dependent on a temperature difference between the measurement electrodes. This later temperature difference cannot be determined using devices known to date.